Attenuation Flashcards
attenuation
the weaking of the sound beam as it travels
clinical importance of attenuation (3)
limits our imaging depth
must be compensated for (TGC/gain)
can be useful in diagnosis
bel/decibel are what
relative units of measurement expressing the loudness (intensity level) of sound waves
1 bel (B) = ____ decibels (dB)
10
0 dB as a percentage for US
100%
instrument ____ uses decibels to determine the ____ of the sound leaving the transducer
output
power
dynamic range used decibels to express the ______ of shades of grey displayed on a monitor
number
gain and TGC use decibels to express the amount of ______ or ______ required to optimize the returning echoes
amplification
attenuation
formula to calculated bels/dB
b=log(new I / original I)
dB=10log (new I / original I)
power formula
dB=10log(new P / original P)
voltage formula
dB=20log(new V / old V)
1/2 original intensity = ___ dB drop
3
.1 of og intensity= ___ dB drop
10
10db drop =
.1 of og intensity
3dB drop=
1/2 original intensity
input/output power = what in power formula
input= Po (original P)
output= Pn (new P)
attenuation coefficient
amount of attenuation that occurs with each one cm travelled
attenuation coefficient in soft tissue
.5 dB for every one cm travelled per 1 MHz
attenuation coefficient in soft tissue is equivalent to _____
1/2 freqeuncy
Total attenuation formula
Tatt= att. coef. x path length (cm)
total attenuation formula for soft tissure
Tatt= 1/2f x path length (cm)
half-value layer is what
the distance sound must travel in a material to reduce the intensity to half its original value
attenuation can vary with the following (3)
nature of tissue (dead/alive)
frequency of the US
depth
half-value layer formula
Tatt=1/2f x path
but
3dB loss= 1/2 og intensity
so
formula=
3dB=1/2f x path